THE IMPORTANCE OF UNDERSTANDING CONCRETE
Air loss can be minimized when pumping by slowing down the “freefall” of the concrete and minimizing the pumping pressure.
When possible, admixtures should be used instead of water to achieve higher slump. Slump loss through the pump can negatively affect pumping. Aggregate will absorb large amounts of water when under the pressure of the pump. This can cause a blockage and be completely unpumpable. Such aggregate should be soaked long enough to achieve Saturated Surface Dry (SSD). SSD aggregate cannot absorb any more water.
Lightweight aggregate is porous with absorption values of up to 20%. This quality requires the aggregate to be thoroughly soaked to minimize the aggregates’ ability to absorb even more water under the pressure of the pump, causing severe slump loss.
Due to the low cement content of flowable fill, the material has a tendency to mechanically set (settle) quickly. When pumping flowable fill, it is important to keep the material moving.